1. Field of the Invention
The invention relates to a device for introducing a liquid or gaseous reactant into a gas flow, having at least one outlet opening for the emergence of the reactant. In particular, the invention may be used with deNOx catalysts in eliminating nitrogen oxides NO.sub.x from flue gases.
In the catalytic removal of nitrogen from flue gases by the SCR process, ammonia (NH.sub.3) must be introduced or "injected" into the flue gas flow. A definitive factor for the extent of catalytic conversion is the uniformity of distribution of the ammonia in the flue gas prior to entry into the SCR catalytic converter. In constructing the flue gas channels and the catalytic converter geometry, the goal is to keep the mixing distances between the ammonia injection and the catalytic converter as short as possible. In that way, the structural height can be kept low, therefore keeping construction costs and finally the pressure losses low as well. In other words, in the "injection" of ammonia into a flue gas stream, or its admixture with the stream, the goal is to provide the completest possible mixing of ammonia and flue gas. However, it is also important to achieve the shortest possible distance between the outlet opening of the reactant and the adjoining catalytic converter.
Heretofore, the problem of complete mixing has been addressed by two different constructions:
1. The ammonia was injected at an adequate distance upstream of a first catalytic converter module plane. Such a "turbulent diffusion" as it is called, that is molecular transport as a consequence of turbulent motion of the flue gas and NH.sub.3 flow, was the primary factor in bringing about mixing of the ammonia with the flue gas flow.
2. Mixer elements or turbulizers were built into flue gas channel between the ammonia injection and the catalytic converter.
Those two different constructions, while they did produce largely uniform mixing, nevertheless have a number of disadvantages: As a rule, long flue gas channels are provided, which entails correspondingly high costs. Often a different ammonia concentration must be added to the gas flow at various outlet openings over the flue gas channel cross section. In the startup phase, that involves relatively major measurement effort and expense, since accurate adjustment of the various ammonia concentrations over the flue gas channel cross section is necessary for the sake of final deNOx operation. When the aforementioned mixer elements were used, that meant additional costs for components and additional pressure losses.